Rotary cutting tools have been proposed with shanks weakened to deliberately localize the point of failure and to provide a protruding shank portion after failure. The shank portion may be engaged by a wrench or other tool to effect removal of the broken tool. Rotary cutting tools have also been proposed with the weakened portion of the shank locally annealed to provide a warning (by a twisting action of the tool) to the operator prior to actual failure. Rotary cutting tools used for drilling bores, cutting internal threads in bores, or otherwise machining a work piece have been fabricated from conventional cold drawn steel blanks. Such tool materials produce limited and uneven wear characteristics.
Another problem associated with such tools is that the warning provided by a locally annealed shank is only useful during manual use. When such a shank twists or otherwise bends to absorb excessive stress during automatic machining operations, the alignment of the cutting portion of the tool with respect to the driving portion of the tool may be altered making the cutting portion off center and causing out of tolerance cutting action and excessive and uneven wear. Still another problem associated with such tools is that the process of deliberately weakening a portion the tool shank with "V" cuts or annealed grooves creates unnecessary and unpredictable weaknesses in the shank making the tool weaker than conventional solid rotary cutting tools. This makes the amount of stress which the shank can withstand before failure difficult to accurately predict. Breakage of the tool often occurs with a shattering action, creating operator hazards such as flying chips and jagged edges.